Sonic flow meter

ABSTRACT

A device for measuring the velocity and direction of flow of a fluid uses a pressure wave signal which is transmitted both upstream and downstream. The resulting signals are mixed to form a single signal having a phase angle representative of the speed and direction of flow.

United States Patent 11113,575,049

[72] Inventor Thomas J. Boland [56] References Cited Idaho Falls, IdahoUNITED STATES PATENTS Qf' 31 1970 2,991,650 7/1961 Katzenstein et al73/194 [45] Patented 1971 3,109,112 10/1963 Lester 73/194 [73] AssigneeThe United States of America as represented 1969 Yoshlyama et 73/ 194 bythe United States Atomic Energy FOREIGN PATENTS Commission 891,5293/1962 Great Britain 73/ l 94 Primary Examiner-Charles A. RuehlAtt0meyRoland A. Anderson [54] SONIC FLOW METER 5 Chums 1 DrawmgABSTRACT: A device for measuring the velocity and [52] US. Cl 73/194direction of flow of a fluid uses a pressure wave signal which is [51]Int. Cl GOlp 5/00 transmitted both upstream and downstream. Theresulting [50] Field of Search 73/194 (A), signals are mixed to form asingle signal having a phase angle 189, 18! representative of the speedand direction of flow.

GENE/P1970? 29 IND/0970f? I SHIF T SONIC FLOW METER CONTRACTUAL ORIGINOF THE INVENTION or under, a contract with the UNITED STATES ATOMICENERGY COMMISSION.

BACKGROUND OF THE INVENTION The velocity of a fluid flowing in a pipecan be measured by measuring the time delay to a signal transmittedthrough the fluid between transducers. If the signal is transmitted inthe direction of flow of the fluid, or downstream, the time delay isless than if the transmission is in the upstream direction. The greaterthe velocity of the fluid the greater the time delay difference whichoccurs. The measurement of the velocity can be made by measuring thephase angle between the transmitted and received signals and subtractingthe phase angle displacement caused by the distance between thetransmitting and receiving transducers.

The phase angle displacement caused by the distance between thetransducers is normally very much greater than the phase angledisplacement caused by the flow of the fluid. Thus the above method issubject to errors because of the uncertainty in distance between thetransducers. In order to cancel out the error, fluid velocity measuringsystems have been devised in which the signal was alternatelytransmitted upstream and downstream. The alternate system approach alsocauses problems. These include a requirement for a near perfect switch;wideband amplifiers to switching pulse shape; and long term integrationto smooth switching transients.

It is therefore an object of this invention to provide an improved flowmeter.

Another object of this invention is to provide a flow meter requiringonly narrow-band amplifiers.

Another object of this invention is toprovide a flow meter in whichlittle or no integration time is required.

SUMMARY OF THE INVENTION In practicing this invention a pair oftransducers are provided located in the stream of flow of the fluid. Anelectrical signal is generated and applied to each of the transducers sothat one pressure wave signal is transmitted upstream and anotherpressure wave signal is transmitted downstream simultaneously. Eachtransducer receives the signal transmitted by the other transducer,develops an electrical signal therefrom and combines it with its owntransmitted signal. The signals at each transducer are further combinedto fon'n a single signal which is amplifier and applied to a phasecomparator. A second input to the phase comparator is a signal having apredetermined phase relationship with the input signal to thetransducers. The phase angles between the two signals applied to thephase comparator are a measure of the speed and direction of flow of thefluid. An indicator may be coupled to the phase comparator to give adirect reading of the speed and direction of flow of the fluid.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in thesingle drawing, a partial schematic and partial block diagram of thecircuit incorporating the features of this invention.

DETAILED DESCRIPTION OF THE INVENTION Any frequency may be used whichcan be transmitted through the fluid between two transducers.

The signal from generator is applied to primary winding 13 oftransformer 11. Secondary windings 14 and 16 of transformer 11 arecoupled to transducers l7 and 19. A

common terminal of secondary windings 14 and 16 is coupled totransducers 17 and 19 through, primary winding 22 of transformer 20.Secondary windings 14 and 16 are connected so that the signals acrossthe windings are 180 out of phase.

A fluid, the velocity of which is to be measured, flows through a pipe23. Transducers 17 and 19 are positioned in pipe 23 so that energytransmitted therebetween flows through the fluid in the same directionas the fluid (downstream) or in the opposite direction (upstream). Thus,in the drawing, energy transmitted from transducer 17 to transducer 19is transmitted downstream, while energy transmitted from transducer 19to transducer 17 is transmitted upstream.

Transducers l7 and 19 convert the electrical signals applied thereto toa pressure wave signal which is transmitted through the fluid in pipe23. An example of a fluid in which velocity measurements were obtainedis an acid dissolver used in chemical processes. However, the fluid isnot limited to an acid but may be any fluid through which a pressurewave signal can be transmitted.

In operation, the pressure wave signal received by transducer 19 iscombined with the signal applied to transducer 19 from secondary winding16. This combined signal is applied to the primary winding 22 oftransformer 20.

, The pressure wave signal received by transducer 17 from transducer 19is combined with the signal from secondary winding 14 applied totransducer 17 and this combined signal is applied to primary winding 22.Because of the phase relationship of secondary windings 14 and 16 oftransformer 11, the signals applied to primary winding 22 of transformer20 are in phase opposition and tend to cancel. If the fluid in pipe 23were stationary, there would be complete cancellation and there would beno resulting signal in secondary winding 24 of transformer 20. If thefluid flows as shown by the direction of arrows in pipe 23, the phaseangle of the combined signal from transducer 17 and the phase angle ofthe combined signal from transducer 19 would be different and thus therewould be a small resulting signal developed in secondary winding 24.

The signal developed in secondary winding 24 is amplified in amplifier25 and applied as one input to a phase comparator 26. The signal fromgenerator 10 is applied to a phase shifter 28 where it is shifted inphase by 90. The output of phase shifter 28 is also applied to phasecomparator 26.

Phase comparator 26, which may be, for example, a balanced modulator,develops a signal having an amplitude and a polarity which is a functionof the phase angle between the two input signals. This phase angle, inturn, is a function of the speed and direction of flow of the fluidthrough pipe 23. This signal may be coupled to an indicator 29 as, forexample, a voltmeter, calibrated to read the fluid velocity directly.

The device described is simple and continuous in operation. The pressurewave signals are transmitted both upstream and downstream simultaneouslyand continuously. Thus there is no requirement for switching andwideband amplifiers are not required to preserve the pulse shape of thesignals. The amplifiers required need have a bandwidth only wide enoughto accommodate any frequency drift in the system. This results in agreatly improved signal-to-noise ratio. Since very little, if any,integration is necessary, the information is available instantaneously.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

Iclaim:

1. A device for measuring the direction and velocity of flow of aliquid, including in combination, first and second transducers spatiallydisposed along the line of flow of the fluid to .permit the mutualtransmission of signals therebetween through the liquid, signalgeneration means coupled to said first and second transducers and actingto develop first and second signals and apply the same to said first andsecond transducers respectively, said first and second signals being lout of phase, said first and second transducers acting to transmit saidfirst and second signals through the liquid as a pressure wave to saidsecond and first transducers respectively, said first signal and saidsecond transmitted signal being combined at said first transducer todevelop a third signal and said second signal and said first transmittedsignal being combined at said second transducer to develop a fourthsignal, signal combining means coupled to said first and secondtransducers and being responsive to said third and fourth signals todevelop a difference signal, and measuring means coupled to said signalgeneration means and said signal combining means, said measuring meansbeing responsive to said difference signal and one of said first andsecond signals to measure the phase angle therebetween, said phase anglebeing a measure ofthe velocity and direction of flow of the liquid.

2. The measuring device of claim 1 wherein, the liquid is confined to apipe with said first and second transducers being positioned within saidpipe.

3. The measuring device of claim 2 wherein, the frequency of said firstand second signals is ultrasonic.

4. The measuring device of claim 3 wherein, said signal generation meansincludes a signal generator for developing an output signal of aparticular phase and frequency and a first transfonner having a primarywinding coupled to said signal generator for receiving said outputsignal therefrom and a pair of secondary windings, said pair ofsecondary windings being connected in series and having a commonterminal, said secondary windings further being connected so that saidfirst signal is developed across one of said secondary windings and saidsecond signal is developed across the other of said secondary windings,said one secondary winding being connected to said first transducer andsaid other secondary winding being connected to said second transducer,said signal combining means including a second transfonner having afirst winding connected to said common terminal and to each of saidfirst and second transducers, and a second winding connected to saidmeasuring means, said second transformer acting to develop saiddifference signal across said second winding in response to said thirdand fourth signals, and circuit means coupling said measuring means tosaid first transformer for receiving a signal therefrom having the phaseof one of said first and second signals.

5. The measuring device ofclaim 4 wherein, said measuring means includesphase-shifting means coupled to said circuit means for shifting thephase of the signal received therefrom by 90 phase comparator meanscoupled to said 90 phase-shifting means and said second winding, saidphase comparator means being responsive to the 90 phase-shifted signaland said difference signal to measure the phase angle therebetween andthereby the velocity and direction of flow of the liquid.

1. A device for measuring the direction and velocity of flow of aliquid, including in combination, first and second transducers spatiallydisposed along the line of flow of the fluid to permit the mutualtransmission of signals therebetween through the liquid, signalgeneration means coupled to said first and second transducers and actingto develop first and second signals and apply the same to said first andsecond transducers respectively, said first and second signals being180* out of phase, said first and second transducers acting to transmitsaid first and second signals through the liquid as a pressure wave tosaid second and first transducers respectively, said first signal andsaid second transmitted signal being combined at said first transducerto develop a third signal and said second signal and said firsttransmitted signal being combined at said second transducer to develop afourth signal, signal combining means coupled to said first and secondtransducers and being responsive to said third and fourth signals todevelop a difference signal, and measuring means coupled to said signalgeneration means and said signal combining means, said measuring meansbeing responsive to said difference signal and one of said first andsecond signals to measure the phase angle therebetween, said phase anglebeing a measure of the velocity and direction of flow of the liquid. 2.The measuring device of claim 1 wherein, the liquid is confined to apipe with said first and second transducers being positioned within saidpipe.
 3. The measuring device of claim 2 wherein, the frequency of saidfirst and second signals is ultrasonic.
 4. The measuring device of claim3 wherein, said signal generation means includes a signal generator fordeveloping an output signal of a particular phase and frequency and afirst transformer having a primary winding coupled to said signalgenerator for receiving said output signal therefrom and a pair ofsecondary windings, said pair of secondary windings being connected inseries and having a common terminal, said secondary windings furtherbeing connected so that said first signal is developed across one ofsaid secondary windings and said second signal is developed across theother of said secondary windings, said one secondary winding beingconnected to said first transducer and said other secondary windingbeing connected to said second transducer, said signal combining meansincluding a second transformer having a first winding connected to saidcommon terminal and to each of said first and second transducers, and asecond winding connected to said measuring means, said secondtransformer acting to develop said difference signal across said secondwinding in response to said third and fourth signals, and circuit meanscoupling said measuring means to said first transformer for receiving asignal therefrom having the phase of one of said first and secondsignals.
 5. The measuring device of claim 4 wherein, said measuringmeans includes 90* phase-shifting means coupled to said circuit meansfor shifting the phase of the signal received therefrom by 90 phasecomparator means coupled to said 90* phase-shifting means and saidsecond winding, said phase comparator means being responsive to the 90*phase-shifted signal and said difference signal to measure the phaseangle therebetween and thereby the velocity and direction of flow of theliquid.